A great place to start your research is Apple's investor relations site. You can find all of their SEC filings, including the quarterly and annual reports. These reports include an overview of the business, financial statements, disclosures of market risk, and much more.
It would help if you considered how much money you have to invest and how big of a part you want Apple to play in your portfolio. As a rule of thumb, stocks should be considered long-term investments. You should only invest money you won't need in the short-term into the stock market.